Electrical recording apparatus



y 7, 1958 E. TRAUB ETAL 2,836,479

ELECTRICAL RECORD ING APPARATUS Filed July 16, 1952 2 Sheets-Sheet lflfifirmaor T0118 M0 ALFRED ORTLIEB BY:

y 7, 1958 E. TRAUB ETAL 2,836,479

ELECTRICAL RECORDING APPARATUS Filed July 16, 1952 2 Sheets-Sheet z X\ II): J'44?L- A2 70 m} a f0 1 M Jec United States Patent ELECTRICALRECORDING APPARATUS Eberhardt Traub and Alfred Ortlieb, Stuttgart,Germany Application July 16, 1952, Serial No. 299,152

19 Claims. (Cl. 346-74 The present invention relates to 'an electricalrecordingapparatus, and more particularly to an apparatus forelectrically recording readings of an instrument.

The present application is a continuation-in-part of the ccpendingapplication, Serial No. 195,372, filed November 13, 1950, for RecordingInstrument With Electrical stylus.

it is an object of the present invention to provide a recordingapparatus of the type described in which the recording line is extremelyfine.

it is another object of the present invention to allow very accuraterecordings to be made.

it is a further object of the present invention to provide means fordetermining the period of the deflections of the recording pointer.

An electrical recording apparatus according to the present inventioncomprises in its broadest aspect a record carrying element consisting ofa dielectric base and a metal coating thereon having a specific surfaceresistance of l to 50 ohms/sq. cm., a recording element having anelectrically conductive recording point, means for moving at least oneof the elements with the recording point of the recording elementpermanently in close proximity to the metal coating of the recordcarrying element, and means for imparting a potential difference to theelectrically conductive recording point and the metal coating whereby atrace of the relative motion between the recording element and therecord carrying element is produced on the metal coating by the electricdischarge between the recording point and the metal coating caused bythe potential difference imparted to the same.

Preferably the metal coating has a specific surface resistance of 2-10ohms/sq. cm.

Preferably the metal coating consists of a zinc cadmium uiloy having azinc content below 30%.

The potential diifcrence between the recording point and the metal.coating preferably does not exceed 50 volts and should be kept evenbelow 14 volts.

in a preferred embodiment of the present invention a current source isconnected tothe electrically conductive recording point and said metalcoating and a condenser is connected in parallel to the current source.

Preferably at least one electrical resistor is inserted between thecurrent source and the electrically conductive recording point and acapacitor is connected in parallel with the electrical resistor.

A preferable embodiment of the present invention comprises incombination a recording element consisting of a dielectric strip and ametal coating having a specific surface resistance of. l50 ohms/sq. cm.,and covering one side of the strip, means for imparting a longitudinalmotion to the strip, a movable pointer forming part of an instrumennthepointer carrying out swinging motions substantially transversely to saidstrip, a needle rigidly secured to the end of the pointer with its pointin close proximity-to, and separated by an air gap from the'metalcoating, and means for imparting a potential difference to the n edleand the metal coating whereby a trace of the ice 2 motion of the pointeris produced on the metal coating by the electrical arc discharge betweenthe point of the needle and the metal coating caused by the potentialdifference imparted to the same.

Preferably means are provided for interrupting the electric currentflowing between the recording point of the metal coating duringpredetermined intervals of time. Preferably a semi-incandescent lamp ora spark gap is mounted in parallel to the recording point and the metalcoating.

In a further development of the present invention the metal coating hasa plurality of substantially parallel insulating lines extending fromone edge of the strip.to points being spaced apart from the other edgeof the strip and the metal coating, and a pair of auxiliary electrodesis arranged so as to contact the metal coating at predetermined places,respectively, a relay being connected in series to the auxiliaryelectrodes so that the relay circuit is interrupted whenever theconductive connection formed by the metal coating between the auxiliaryelectrodes is interrupted by the trace produced in the metal coating.Preferably the auxiliary electrodes have a width being larger than theWidth of the insulating lines on the metal coating. Preferably each ofthe auxiliary electrodes consists of two parts, preferably thin wires,having different lengths, connected in parallel, the two parts of wiresbeing arranged relatively to each other so that when one of them ismoving across one of the insulating lines, the other one of the parts orwires is in contact with the metal coating.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the the accompanying drawings,in which Fig. 1 is a perspective view of the recording mechanismaccording to the invention together with wiring diagrams of theelectrical circuits connected thereto;

Fig. 2 is a similar view of another embodiment of the invention;

Fig. 3 is a similar view of a modification of Fig. 2;

Fig. 4 is a similar view of still another modification of the presentinvention;

Fig. 5 is a cross-section on an enlarged scale of a part of Fig. 4;

Fig. 6 is a diagram for explaining the operation of the device shown inFig. 4;

Fig. 7 is a plan view on an enlarged scale of the recording elementshown in Fig. l; and

' Fig. 8 is a side elevation, partly in section, on an enlarged scale ofpart of Fig. 5 and one of the auxiliary electrodes.

Referring now to the drawings and first to Fig. 1, a record-carryingelement 10 consists of a dielectric base or strip 12 shown on anenlarged scale in Figs. 5 and 8 and a metal coating 14 having a specificsurface resistance of l to 50 ohms/sq. cm. and preferably of 2 to 10ohms/sq. cm. The measurement of these resistance values is preferablycarried out by placing two measuring electrodes spaced apart from eachother by 1 cm. on a strip having a Width of 1 cm. and being metallizedby depositing the metal from the vapor state or by cathodic evaporation.If the resistance values mentioned hereinabove are ascertained accordingto this method the thickness of the metal coating 14 is in the order of0.3 to 0.002 microns.

It has been discovered that only within the limits of the specificsurface resistance given hereinabove is 3 obtained the special advantageof the metal coating 14 for recording purposes as to a faithfulreproduction of the amplitudes as more fully described hereinafter.Metal coatings having a higher specific surface resistance involve thedrawback that they have too low a mechanical resistance. On the otherhand, metal coatings having a lower specific surface resistance, allowonly very low speeds of recording. However, with metal coatings having aspecific surface resistance of l to 50 ohms/sq. cm. a small power issufficient for burning or melting the metal so as to obtain a cleanrecord even if the record ing speed and the amplitude to be recorded aresubject to a great deal of fluctuations. This is particularly importantin case quantities have to be recorded which are subject to a very fastchange in time and with large amplitude so that in order to obtain asufficient resolving power a large speed of the dielectric strip 12 isnecessary. The recording speed being the vector sum of the speed of thedielectric strip and the speed which causes the deflection of the needle36 more fully described hereinafter, can reach considerable values, forinstance of m./sec. and more.

Furthermore, the very small thickness of the metal coating 14 allows toinsert into the electric circuit more fully to be described hereinafterresistors, condensers, inductors or combinations of the same which aremore fully disclosed with reference to Fig. 6 and owing to the low powerneeded for the recordinng have to be dimensioned for a low load. Alsothe current sources have to supply only a low power. All these factorscooperate in rendering the recording line 40 or 40 more fully to bedescribed hereinafter very uniform so that the metal coating 14 issubdivided over the entire length of the recording line 46 into twoparts 42 and 44 more fully described hereinafter and electricallyinsulated against each other. This is important with regard to theevaluating methods more fully described hereinafter with respect tocombinations with control devices such as those more fully describedhereinafter which all require for their operation a clean saparation ofthe parts 42 and 44 by the recording line 40 and/or an exact definitionof the distance of the recording line 40 from the edge 82 shown in Fig.7 of the strip 12 or another reference line.

The metal coating 14 covers one side of the strip 12 so as to metallizethe same. The strip 12 is flexible and is moved over a roller 16 in thelongitudinal direction of the strip 12 by a suitable driving means (notshown) so that the recording element 10 moves in the direction of thearrow 18. Another roller 20 is arranged parallel to and at a shortdistance from the roller 16, the recording element 16 forming anS-shaped curve and being touched by the rollers 16 and 20, respectively,on the side of the strip 12 and the side of the metal coating 14. Theroller 16 consists preferably of dielectric material whereas the roller20 consists of electroconductive material, for instance carbon, and isin conductive connection with the metal coating 14. The axle 22 of theroller 2i is connected by a wire 24 to the positive terminal of acurrent source 26 the negative terminal of which is connected by a wire28 to the bearing 30 of an axle 32 forming part of a measuringinstrument (not shown). The current source 26 is preferably a batterysupplying a voltage of less than 50 volts and preferably less than 14volts. The bearing 30 and the axle 32 are made from electricallyconductive material. The axle 32 carries a pointer 34 also made ofelectrically conductive material and carrying at its free end a metalneedle 36 arranged with the point thereof in close proximity to themetal coating 14 and is preferably in sliding contact with the same.

The operation of the device so far described is as follows:

When the roller 16 moves in the direction of the 4 1 curved arrow 38 thedielectric strip 12 of the record carrying element 10 with the metalcoating 14 moves in the direction of the arrow 18, that is, inlongitudinal direction of the recording element 10. Simultaneously thepointer 44 of the measuring instrument (not shown) carries out swingingmotions substantially transversely to the recording element 10 and themetal coating 14. Furthermore, a potential difference is imparted by thecurrent source 26 to the needle 36 of the pointer 34 and the metalcoating 14, the needle 36 being preferably connected to the negativeterminal of the current source 26 and the metal coating 14 over theroller 20 to the positive terminal of the current source 26. Inconsequence thereof a discharge of electric current is caused betweenthe needle 36 and the metal coating 14 which produces in the metalcoating an insulating line 40 according to the positions of the pointer34 and subdividing the metal coating into two parts 42 and 44 beingseparated from each other by the line 40. Since the metal coating 14 isextremely thin, its thickness being in the order of 0.3 to 0.002microns, the needle 36 will burn an extremely fine line 40 into themetal coating 14 which has well-defined margins and is free of slag,beads of molten metal and other irregularities.

Referring now to Fig. 2 a current source is connected to the primarywinding 52 of a transformer 54. The primary winding 52 is connected inseries to a buzzer 56 being under the influence of a restoring spring58. The secondary winding 60 of the transformer 54 has many more turnsthan the primary winding 52 and is connected to the bearing 30 and theaxle 22 of the roller 20. The needle 36 of the pointer 34 is not incontact with the metal coating 14 but is separated from the same by asmall air gap across which a spark discharge is initiated by the voltageinduced in the secondary 60 of the transformer 54 which has a very highvalue owing to the periodical sudden interruption of the primary currentflowing in the primary winding 52. When the secondary voltage disappearsthe spark discharge is extinguished. Thus the line 40 formed on themetal coating 14 consists of a succession of separate markings insteadof a continuous line such as 40 shown in Fig. 1.

A semi-incandescent lamp 62is connected across the secondary 60. Thesemi-incandescent lamp 62 can be omitted; however, it should be providedif the speed of the deflection of the pointer 34 is large because thesemiincandescent lamp 62 aids in obtaining very uniform recordingmarkings on the metal coating 14.

Referring now to Fig. 3 showing a modification of Fig. 2, thesemi-incandescent lamp 62 is replaced by a spark gap 64 having the sameeffect as the semi-incandescent lamp 62.

The embodiments according to Figs. 2 and 3 are used if the friction ofthe needle 36 on the metal coating 14 would cause an inadmissibledampening of the motion of the pointer 34 of the instrument. The recordcarrying element 10 can be moved as in the embodiments according toFigs. 2 and 3 at a distance apart from the needle 36 which amounts to afew tenths of a millimeter, so that the needle 36 is not in touch withthe metal coating 14. However, the spark generated between the needleand the metal coating has suficient energy in view of the smallthickness of the metal coating to record a continuous and cleanrecording line 40. In this arrangement the voltage has to be higher thanthe limiting voltage of the arc, i. c. it has to be at least 14 volts.

Referring now to Fig. 4 the axle 32 of the measuring instrument isprovided with a spiral spring urging the axle 32 into a rest position inwhich the pointer 34 is not deflected. The needle 36 consists oftungsten or platinum wire having a diameter of preferably 0.15 mm. Inconsequence thereof the needle 36 rests on the record-carrying element10 and especially on the metal coating 14 thereof with a very lowpressure so that only very little friction prevails between the metalcoating 14 and the point of the needle 36.

The structure of the record carrying element is shown on an exaggeratedscale in Fig. 5. The strip 12 consists preferably of paper having athickness of about 0.03 mm. and carries a metal coating 14 consistingpreferably of zinc and having a thickness of approximately 0.03 micronsso that the metal coating 14 has a specific surface resistance of about4 ohms/sq. cm.

The carbon roller is connected to the positive terminal of a battery 26supplying a voltage of about 30 volts. The negative terminal of thebattery 26 is connected to the bearing 30 over a resistor 112 havingpreferably a resistance of about 400 ohms. The resistor 112 is shuntedby a capacitor 114 of about 1p. f. Since the needle 36 is very thin ahigh current density is generated at the point of the needle whichcauses a large Joule heat which is only slightly carried away by themetal coating 14 owing to the slight thickness thereof so that the Jouleheat is sufficient, even at a high recording speed, for burning arecording line 40 into the thin metal coating 14.

The line 40 is burned into the metal coating 14 as follows: If thebattery 26 is switched in at first a current flows through the metalcover 14 and the needle 36 which is determined by the magnitude of thevoltage of the battery 26 and the resistances of the circuit such asthat of resistor 112. This current melts, and sometimes even evaporates,the metal surrounding the point of the needle 36. By this the electricalresistance between the needle 36 and the metal coating 14 is increasedso .that the current decreases and is eventually entirely interrupted atthe disappearance of the last portion of the molten metal if the recordcarrying element 10 and the needle 36 do not carry out any relativemotion. If, however, the record carrying element 16 is continually movedin the direction of the arrow 18 during the burning process, the needle36, even if it is not deflected, comes into contact with fresh portionsof the metal coating 14 so that a continuous recording line 40 isgenerated. During this process a mean burning current I prevails whichresults from current impulses following one another and diminishingquickly to zero. 'Fig. 6 shows two curves representing the mean burningcurrent I measured in ma. plotted against the It will be seen from thesecurves that the battery 26 can be dimensioned for a very low power atthese extremely thin metal coatings. For instance at a recording speedof 0.5 meters/sec. and a thickness of the zinc coating of 0.012 micronsthe battery 26 has to supply a load of 36 volts. 4 ma.=0.l44 watts. Thecurrent impules generated at the moment at which the needle 36 touchesthe not yet melted portions of the zinc covering 14 can increase up tothe 30 fold value of the mean current I. In

order to render possible a dimensioning of the battery 26 for the meancurrent I preferably a condenser 116 having a capacity of about 10a t.is connected in parallel to the battery 26, the condenser 116 operatingas an energy storing element. The condenser 116 has to be provided ifthe battery 26 is replaced by an alternating cur- 7 rent source and arectifier dimensioned for the mean current I.

Since the energy used for burning the line 40 is very small in thedevice shown in Fig. 4 the current can be interrupted by a switchconsisting of a movable switch arm 72 actuated by a return force exertedin a conventional manner (not shown) and by a rotating cam disc 74 so asto open and close the switch 70 once per revolution of the cam disc 79.The switch 70 interrupts the current at a low loading of the contactsthereof even with a high switching frequency. The line 40 is thusinterrupted a predetermined number of times during unit time, c. g. asecond, so that the period of the oscillations of the pointer 34 can beread with great accuracy from the line 40 traced in the metal coating14.

As particularly suitable for the recording described hereinabove havebeen found beside the metal coating consisting of zinc metal coatingsconsisting of cadmium and more especially of an alloy of Zinc andcadmium having a zinc content not exceeding 30% because the latter havea particularly low melting point (not exceed ing 500 C.) and thus admitof the use of small voltages of less than 10 volts. Also, the metalcoatingsconsisting of zinc cadmium alloys involve a further advantagethat they are very resistant to atmospheric influences. Record carryingelements having a zinc cadmium coating the thickness of which amounts toabout 0.01 micron can be stored for a long time without appreciabledisintegration of the material of the metal coating.

Referring now to Figs. 7 and 8 and to the right-hand portion of Fig. 1,the metal coating 14 is provided with a plurality of equidistantsubstantially parallel insulating lines extending from one edge 82 ofthe strip 12 and the metal coating 14 to points spaced apart from theother edge 84 of the strip 12 and the metal coating 14. At least onepair of auxiliary electrodes 86 and 88 is arranged so as to contact themetal coating 14 at predetermined places shown in the drawings atopposite sides of the line 40. A current source 90 and a relay 92 areconnected in series to the auxiliary electrodes 86 and 88.

The operation of this device is as follows:

The relay circuit 90, 92 remains closed as long as the two electrodes 86and 88 are condnctively connected by the metal coating 14 so that therelay 92 is energized. If, however, the pointer 34 is deflected to suchan extent that the recording line 40 lies between the auxiliaryelectrodes 86 and 88 as shown in Figs. 1 and 7, the conductiveconnection thereof is severed and the relay circuit will be interruptedso that the relay 92 is de-energized and actuates in consequence thereofa contact 94, operating switches or signalling means (not shown).

If the relay 92 is only to be de-energized if the pointer 34 hasremained in the deflected position thereof for a predetermined timeinterval, two additional auxiliary electrodes 96 and 98 have to beconnected in parallel with the auxiliary electrodes 86 and 88,respectively. The auxiliary electrodes 96 and 98 are arranged at acertain distance from the auxiliary electrodes 86and 88, said distancecorresponding to the predetermined time interval. If the pointer 34swings back within the predetermined time interval, the recording line40 will follow a course passing between the auxiliary electrodes 86 and88 but not between the auxiliary electrodes 96 and 98 so that the relay92 remains energized.

Preferably the auxiliary electrodes such as 86 have a width which iswider than the width of the insulating line, 80, this being indicated inPig. 7. Freferably each auxiliary electrode such as 86, as shown in Fig.8 consists of two parts such as two thin wires 100 and 102 of differentlengths and connected in parallel which are so spaced from each otherthan when the auxiliary electrode such as 86 passes from one metallizedsubdivision 104 to the following one 106 one of the wires (100) is stillin contact with the subdivision 104 while the other wire 102 is passingthe insulating line 80 or is even in contact with the followingmetallized subdivision 106.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofelectrical recording apparatuses differing from the types describedabove.

reveal the gist of the present invention that others can by applyingcurrent knowledge readily adapt it for various applications withoutomitting features that, from the standpoint of prior art, fairlyconstitute essential characteristics of the generic or specific aspectsof this invention and, therefore, such adaptations should and areintended to be comprehended within the meaning and range of equivalenceof the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

l. In an electrical recording apparatus, in combination, a recordcarrying element consisting of a dielectric base and a metal coatingthereon having a specific surface resistance of 2-l0 ohms per squarecentimeter; a recording element having an electrically conductiverecording point; means for moving at least one of said elements withsaid recording point of said recording eleent permanently in closeproximity to said metal coating of said record carrying element; andmeans for imparting a potential difference not exceeding 36 voltsbetween said electrically conductive recording point and said metalcoating whereby any electric discharge between said recording point andsaid metal coating caused by said potential difference produces a traceof the relative motion between said recording element and said recordcarrying element on said metal coating.

2. In an electrical recording apparatus, in combination, a recordcarrying element consisting of a dielectric base and a metal coatingthereon having a specific surface resistance of l to 50 ohms per squarecentimeter, said metal having a melting point not exceeding 500 C; arecording element having an electrically conductive recording point;means for moving at least one of said elements with said recording pointof said recording ele ment permanently in close proximity to said metalcoating of said record carrying element; and means for imparting apotential difference of less than 50 volts between said electricallyconductive recording point and said metal coating whereby any electricdischarge between said recording point and said metal coating caused bysaid potential dilference producesa trace of the relative motion betweensaid recording element and said record carrying element on said metalcoating.

3. In an electrical recording apparatus, in combination, a recordcarrying element consisting of a dielectric base and a metal coatingthereon having a specific surface esist-ance-of l to 50 ohms per squarecentimeter; said metal consisting of a zinc cadmium alloy having a zinccontent being below a recording element having an electricallyconductive recording point; means for moving at least one of saidelements with said recording point of said recording element permanentlyin close proximity to said metal coating of said record carryingelement; and means for imparting a potential difference of less thanvolts between said electrically conductive recording point and saidmetal coating whereby any electric discharge between said recordingpoint and said metal coating caused by said potential differenceproduces a trace of the relative motion between said recording elementand said record carrying element on said metal coating.

4. In an electrical recording apparatus, in combination, a recordcarrying element consisting of a dielectric base and a metal coatingthereon having a specific surface resistance of 1 to 50 ohms per squarecentimeter; a recording element having an electrically conductiverecording point; means for moving at least one of said elements withsaid recording point of said recording element permanently in colseproximity to said metal coating of said record carrying element; andmeans for 'irnparting a potential difierence, not exceeding 50 voltsbetween said electrically conductive recording point and said metalcoating whereby any electric discharge between said recording point andsaid metal coating caused by said potential direrence produces a traceof the relative motion between said recording element and said recordcarrying element on said metal coating.

.r electrical recording apparatus, in combinarecord carrying elementconsisting of a dielecelement having electrically con-d ctive means formoving at least one of said clc r recording point of said recordingcler. rmanently close proximity to said rncal costsaid record carryingelement; and means ror im- -ttng potential difference, not exceeding 14voits een said electrically conductive recording point metal coatingwhereby any electric dis harge between said recording point and saidmetal coating cs by said potential dill" fence produces a trace of 't te motion between said recording element record carrying element on saidmetal coating.

.6. in an electrical recording appar tus, in corn tion, a recordcarrying element consi 'ng of a tric base and a metal coating thereonhaving a surface resistance of l to 50 ohms per n rc centimeter; arecording element having an elec y conductive recording poir.; means formoving a least of s elements with said recording point of said ecordingc1 ment permanently close oroximity to said metal ccating of said recordcarryi element; t source connected to said electrically CC/lMiCc werecording point and said metal coating; and a storage condenserconnected in parallel with said direct current sourc whereby a potentialdifference not exceeding 55) volts imparted between said electricallyconductive recording point and said metal coating so that a trace of therelative motion between said recording element and said record carryingelement is produced on said metal coating by the electric dischargecurrent between s.id recording point and said metal coating caused bythe potential dir'ierencc imparted to the same, said direct currentsource being dimensioned to provle the mean electric discharge currentproduced between said recording point and said metal coating.

7. In an electrical recording apparatus, in combination, a recordcarrying element consisting of a dielectric base and a metal coatingthereon having a spec surface resistance of l to 50 ohms per squarecentimeter, said metal consisting of a Zinc cadmium alloy having a zinccontent being below 30%; a recording element haing an electricallyconductive recording point; means for moving at least one of saidelements with d record ing point of said recording element permane; inclose proximity to said metal coating of said record carrying element;energizing means for imparting a po ential diflerence between saidelectrically conductive recording point and said metal coating whereby atrace of the relative motion between said recording element and saidrecord carrying element is produced on said metal coating by theelectric discharge between said recording point and said metal coatingcaused by said potential d f erence; and at least one resistor connectedin circuit with said energizing means for regulating said potentialdifference.

8. In an electrical recording apparatus, in combination, a recordcarrying element consisting of a dielectric base and a metal coatingthereon having a specific surface resistance of 1 to 50 ohms per squarecentimeter; a recording element having an electrically conductiverecording point; means for moving at least one of said elements withsaid recording point of said recording, element permanently in closeproximity to said metal coating of said record carrying element; adirect current source connected to said electrically conductiverecording point and said metal coating whereby a potential differencenot exceeding 50 volts is imparted between said electrically conductiverecording point and said metal coating so that a trace of the relativemotion between said recording element and said record carrying elementis produced on said metal coating by the electric discharge between saidrecording point and said metal coating caused by the potentialdifference imparted to the same; at least one electrical resistorconnected in series between said current source and said electricallyconductive recording point; and a storage condenser connected inparallel with said direct current source, at least one plate of saidcondenser being connected between said resistor and said current source.

9. In an electrical recording apparatus, in combination, a recordcarrying element consisting of a dielectric base and a metal coatingthereon having a specific surface resistance of 1 to 50 ohms per squarecentimeter; a recording element having an electrically conductiverecording point; means for moving at least one of said elements withsaid recording point of said recording element permanently in closeproximity to said metal coating of said record carrying element;energizing means for imparting a potential difierence between saidelectrically conductive recording point and said metal coating whereby atrace of the relative motion between said recording element and saidrecord carrying element is produced on said metal coating by theelectric discharge between said recording point and said metal coatingcaused by said potential difierence; and at least one rcsistor andcapacitor connected in parallel with each other and in circuit with saidenergizing means for regulating said potential dilference.

10. In an electrical recording apparatus, in combination, a recordcarrying element consisting of a dielectric base and a metal coatingthereon having a specific surface resistance of l to 50 ohms per squarecentimeter; a recording element having an electrically conductiverecording point; means for moving at least one of said elements withsaid recording point of said recording element permanently in closeproximity to said metal coating of said record carrying element; acurrent source connected to said electrically conductive recording pointand said metal coating; a condenser connected in parallel with saidcurrent source whereby a potential difference not exceeding 50 volts isimparted to said electrically conductiverecording point and said metalcoating so that a trace of the relative motion between said recordingelement and said record carrying element is produced on said metalcoating by the electric discharge between said recording point and saidmetal coating caused by the potential ditference imparted to the same;at least one electrical resistor inserted between said current sourceand said electrically conductive recording point; and a capacitorconnected in parallel with said electrical resistor.

ll. In an electrical recording apparatus, in combination, a recordcarrying element consisting of a dielectric base and a metal coatingthereon having a specific surface resistance of 1 to 50 ohms per squarecentimeter; a recording element having an electrically conductiverecording point; means for moving at least one of said elements withsaid recording point of said recording element permanently in closeproximity to said metal coating of said record carrying element; meansfor imparting a potential dilference to said electrically conductiverecording point and said metal coating so as to cause an electriccurrent to flow between the same tracing on said record carrying elementa trace of the relative motion between said recording element and saidrecord carrying element; and means for interrupting said currentperiodically during predetermined intervals of time.

12. In an electrical recording apparatus, in combination, a recordcarrying element consisting of a dielectric base and a metal coatingthereon having a specific surface resistance of.l to 50 ohms per squarecentimeter; a recording element having an electrically conductiverecording point; means for moving at least one of said elements withsaid recording point of said recording element permanently in closeproximity to said metal coating of said record carrying element; meansfor imparting a potential dilference to said electrically conductiverecording point and said metal coating so as to cause an electriccurrent to flow between the same tracing on said record carrying elementa trace of the relative motion between said recording element and saidrecord carrying element; and means for closing and interrupting saidcurrent periodically during predetermined short intervals of time.

13. In an electrical recording apparatus, in combination, a recordcarrying element consisting of a dielectric base and a metal coatingthereon having a specific surface resistance of 1 to 50 ohms per squarecentimeter; a recording element having an electrically conductiverecording point; means for moving at least one of said elements withsaid recording point of said recording element permanently in closeproximity to said metal coating of said record carrying element; meansfor imparting a potential difierence to said electrically conductiverecording point and said metal coating so as to cause an electriccurrent to flow between the same tracing on said record carrying elementa trace of the relative motion between said recording element and saidrecord carrying element; and means for interrupting said current duringpredetermined intervals of time.

14. In an electrical recording apparatus, in combination, a recordcarrying element consisting of a dielectric base and a metal coatingthereon having a specific surface resistance of l to 50 ohms per squarecentimeter; a recording element having an electrically conductiverecording point; means for moving at least one of said elements withsaid recording point of said recording element permanently in closeproximity to said metal coating of said record carrying element; meansfor imparting a potential difference to said electrically conductiverecording point and said metal coating so as to cause an electriccurrent to flow between the same tracing on said record carrying elementa trace of the relative motion between said recording element and saidrecord carrying element; means for interrupting said current duringpredetermined intervals of time; and a semi-incandescent lamp connectedin parallel to said electrically conductive recording point and saidmetal coating.

15. In an electrical recording apparatus, in combination, a recordcarrying element consisting of a dielectric base and a metal coatingthereon having a specific surface resistance of 1 to 50 ohms per squarecentimeter; a recording element having an electrically conductiverecording point; means for moving at least one of said elements withsaid recording point of said recording element permanently in closeproximity to said metal coating of said record carrying element; meansfor imparting a potential ditference to said electrically conductiverecording point and said metal coating so as to cause an electriccurrent to flow between the same tracing on said record carrying elementa trace of the relative motion between said recording element and saidrecord carrying element; means for interrupting said current duringpredetermined intervals of time; and a spark gap connected in parallelto said electrically conductive recording pointand said metal coating.

16. Apparatus for electrically recording readings of an instrument,comprising, in combination, a recording element consisting of adielectric strip and a metal coating having a specific surfaceresistance of 1 to 50 ohms per square centimeter and covering one sideof said strip; a plurality of equidistant substantially parallelinsulating lines extending over said metal coating from one edge of saidstrip to points being spaced apart from the other edge of said strip andsaid metal coating; means for imparting a longitudinal motion to saidstrip; a movable pointer forming part of said instrument, said pointercarrying out swinging motions substantially transversely to said strip;a needle rigidly secured to the end of said pointer with its point inclose proximity to said metal coating; means for imparting a potentialdifierence to said needle and said metal coating whereby a trace of themotion of said pointer is produced on said metal coating by theelectrical discharge between said point of said needle and said metalcoating caused by the potential difierence imparted to the same; a pairof auxiliary electrodes being arranged so as to contact said metalcoating at predetermined places, respectively; and a relay connected inseries to said auxiliary electrodes so that the circuit in said relay isinterrupted whenever the conductive connection formed by said metalcoating between said auxiliary electrodes is interrupted by said traceproduced in said metal coating.

17. Apparatus for electrically recording readings of an instrument,comprising, in combination, a recording element consisting of adielectric strip and a metal coating having a specific surfaceresistance of 1 to 50 ohms per square centimeter and covering one sideof said strip; a plurality of equidistant substantially parallelinsulating lines extending over said metal coating from one edge of saidstrip to points being spaced apart from the other edge of said strip andsaid metal coating; means for imparting a longitudinal motion to saidstrip; a movable pointer forming part of said instrument, said pointercarrying out swinging motions substantially transversely to said strip;a needle rigidly secured to the end of said pointer with its point inclose proximity to said metal coating; means for imparting a potentialdifference to said needle and said metal coating whereby a trace of themotion of said pointer is produced on said metal coating by theelectrical discharge between said point of said needle and said metalcoating caused by the potential difierence imparted to the same; a pairof auxiliary electrodes being arranged so as to contact said metalcoating at prede termined places, respectively, said auxiliaryelectrodes having a width being larger than the width of said insulatinglines on said metal coating; and a relay connected in series to saidauxiliary electrodes so that the circuit in said relay is interruptedwhenever the conductive connection formed by said metal coating betweensaid auxiliary electrodes is interrupted by said trace produced in saidmetal coating.

18. Apparatus for electrically recording readings of an instrument,comprising, in combination, a recording element consisting of adielectric strip and a metal coating having a specific surfaceresistance of 1 to 50 ohms per square centimeter and covering one sideof said strip; a plurality of equidistant substantially parallelinsulating lines extending over said metal coating from one edge of saidstrip to points being spaced apart from the other edge of said strip andsaid metal coating; means for imparting a longitudinal motion to saidstrip; a movable pointer forming part of said instrument, said pointercarrying out swinging motions substantially transversely to said strip;a needle rigidly secured to the end of said pointer with its point inclose proximity to said metal coating; means for imparting a potentialdifference to said needle and said metal coating whereby a trace of themotion of said pointer is produced on said metal coating'by theelectrical discharge between said point of said needle and said metalcoating caused by the potential difference imparted to the same; a pairof auxiliaryelectrodes being arranged so as to contact said metalcoating at predetermined places, respectively, each of said auxiliaryelectrodes consisting of two parts connected in parallel, said two partsbeing arranged relative to each other so that when one of said parts ismoving across one of said insulating lines, the other one of said partsis in contact with said metal coating; and a relay connected in seriesto said auxiliary electrodes so that the circuit in said relay isinterrupted whenever the conductive connection formed by said metalcoating between said auxiliary electrodes is interrupted by said traceproduced in said metal coating.

19. Apparatus for electrically recording readings; of an instrument,comprising, in combination, a recording element consisting of adielectric strip and a metal coating having a specific surfaceresistance of 1 'to 50 ohms per square centimeter and covering one sideof said strip; a plurality of equidistant substantially parallelinsulating lines extending over said metal coating from one edge of saidstrip to points being spaced apart from the other edge of said strip andsaid metal coating; means for imparting a longitudinal motion to saidstrip; a movable pointer forming part of said instrument, said pointercarrying out swinging motions substantially transversely to said strip;a needle rigidly secured to the end of said pointer with its point inclose proximity to said metal coating; means for imparting a potentialdifierence to said needle and said metal coating whereby a trace of. themotion of said pointer is produced on said metal coating by theelectrical discharge between said point of said needle and said metalcoating caused by the potential difierence imparted to the same; a pairof auxiliary electrodes being arranged so as to contact said metalcoating at predetermined places, respectively, each of said auxiliaryelectrodes consisting of two thin wires having difierent lengths andbeing connected in parallel, said two wires being arranged relative toeach other so that when one of said wires is moving across one of saidinsulating lines, the other one of said wires is in contact with saidmetal coating; and a relay connected in series to said auxiliaryelectrodes so that the circuit in said relay is interrupted whenever theconductor connection formed by said metal coating between said auxiliaryelectrodes is interrupted by said trace produced in said metal coating.

References Cited in the file of this patent UNITED STATES PATENTS912,181 Schattner Feb. 9, 1909 1,651,074 Steffens Nov. 29, 19272,250,102 Klemperer July 22, 1941 2,435,441 Grouse Feb. 3, 19482,443,647 Waterman June 22, 1948 2,457,131 Curtis Dec. 28, 19482,547,074 Cirlin Apr. 3, 1951 2,569,414 Godley Sept. 25, 1951 2,572,668Russell Oct. 23, 1951 FOREIGN PATENTS 17,388 Great Britain 1912 904,381France Nov. 5, 1945

